This long-term project is concerned with identifying brain mechanisms involved in species-typical, prosematic (rudimentary signaling) communication. The mirror display (which is a highly predictable variation of a naturally occurring display used by gothic-type squirrel monkeys) provides a means of testing the effects of brain lesions on various elements of the display. Previous experiments revealed that the medial pallidal segment of the striatal complex, as well as the projections of this segment to the thalamus and to the tegmentum, play a basic role in the display. Tegmental lesions were often complicated by damage to the red nucleus, which is the origin of three evolutionary ancient descending systems. In the present project we are attempting to find out whether or not the red nucleus is implicated in the display.